As the density of transistors and circuits in integrated circuit devices increases, thermal management of the integrated circuit device at the package and component levels is becoming more and more critical to the performance and longevity of the integrated circuit device. With the increasing demand for computing power, integrated circuit devices such as microprocessors are becoming more complex, and the number of processing cores integrated into a single chip is also increasing. As a result, integrated circuit dies such as microprocessor dies are becoming physically larger, and consequently, integrated circuit packages are also becoming larger, because larger package substrates are required to accommodate the larger dies. With larger integrated circuit packages, larger package level heat dissipation devices are needed to adequately cool the integrated circuit devices. Also, as the complexity of the integrated circuit devices increases, the number of socket contacts also continues to grow. With a greater number of socket contacts, a higher socket loading force is required to secure the integrated circuit package into a socket. The impact of larger packages and higher socket loads is an increase in the warpage of the package level heat dissipation device such as an integrated heat spreader (IHS).
FIG. 1 illustrates a cross section view of an integrated circuit package 100 before a component level heat dissipation device, such as a heat sink, is attached to the integrated circuit package 100. In the integrated circuit package 100, a package level heat dissipation device such as an integrated heat spreader (IHS) 150 is placed above an integrated circuit die 140 to provide a low thermal resistance path between the integrated circuit die 140 and a component level heat dissipation device above the IHS 150. During operation of the integrated circuit device, heat generated in the integrated circuit die 140 is dissipated through the IHS 150 up towards the component level heat dissipation device. To increase the thermal transfer efficiency and to provide adhesion between the IHS 150 and the component level heat dissipation device above the IHS 150, a thermal interface material (TIM), such as a phase change material or a thermal grease material that has a tendency to flow, is disposed on the top surface of the IHS 150 before the component level heat dissipation device is attached to the integrated circuit package 100. A layer of TIM 141 is also placed between the integrated circuit die 140 and the IHS 150.
FIG. 2 illustrates an integrated circuit package assembly 200 that shows the warpage of an IHS 150 after an integrated circuit package 100 has been inserted and secured in the socket 120, and after a heat sink 170 has been attached to the integrated circuit package 100. In socketed applications, an independent loading mechanism (ILM), which includes a load plate 181 and a retention frame 182, applies a downward force at the step 154 along the edges of the IHS 150 to secure the integrated circuit package 100 into the socket 120. Furthermore, the IHS 150 is also subjected to additional downward loading forces around the edges of the IHS 150 when the heat sink 170 is secured to the integrated circuit package 100 with connectors 183 that are mounted from the heat sink 170 onto the retention frame 182 of the ILM and/or onto the printed circuit board (PCB) 110 at attachment points overhanging the IHS 150. As a result of these downward forces from the ILM and the heat sink 170 being applied to the edges of the IHS 150, the top side of the IHS 150 can be warped when the integrated circuit package assembly 200 is assembled, creating a convex warpage on the top side of the IHS 150 as shown. The warpage, which is defined as the difference in height at the highest point 180A and the lowest point 180B on the top side of the IHS 150, can be over 100 microns (um).
The TIM 160 between the IHS 150 and the heat sink 170 tends to migrate outwards over the edge of the IHS 150 when the integrated circuit package 100 undergoes reliability testing such as shock, vibration, high temperature bake, and temperature cycling. The top side IHS 150 warpage exacerbates this migration, which in turn, causes empty voids 190 or air pockets between the IHS 150 and the heat sink 170. These voids 190 can cause severe degradation in the cooling capability of the heat sink 170, because with the formation of these voids 190, there is less surface area to transfer heat generated from the integrated circuit die 140 through the IHS 150 to the heat sink 170. For example, the degradation in the cooling capability can be on the order of 0.04 degrees Centigrade per Watt, and for a 125 Watt integrated circuit device, this degradation translates to an increase of 5 degrees Centigrade in the operating temperature of the integrated circuit device. Consequently, this leads to slower performance of the integrated circuit device and shortens the longevity of the integrated circuit device.